Chemical vapor infiltration (CVI) and chemical vapor deposition (CVD) are well-known processes for forming composite materials. CVI/CVD are particularly useful processes for fabricating structural composites such as brake disks, combustors and turbine components, and CVD/CVI are also used to fabricate various semiconductor products and other electronic parts. In general, the term CVI implies deposition of a matrix within the pores of a substrate, and the term CVD implies deposition of a surface coating on a substrate. However, as used herein, both terms are intended to refer generally to infiltration and/or deposition of a material on or within a substrate.
In general, CVD is a process of subjecting a substrate to a material in vapor form, resulting in a deposition of the material on the substrate. CVD may be performed at various temperatures and pressures, and for various periods of time. In many applications, CVD is performed at high temperatures and under low pressures, including under a vacuum or near vacuum. To facilitate high temperatures, CVD may be performed in a furnace or other suitable vessel. In many applications, CVD is performed on multiple substrates concurrently for economic and efficiency reasons. To facilitate uniform application of vapor material onto a substrate, the flow rate, direction, duration, and dispersion of the vapor material may be controlled.
CVD may be used to deposit material onto substrates of various shapes and configurations, including annular disks. In such applications, the vapor material (i.e., chemicals in gaseous form) may be released into the vessel via a central tube that is disposed perpendicular to the surface of the annular disks. Vapor material is released into a vessel using various methods. In conventional systems, gas is released through nozzles or holes that are typically located on a central tube or on a plate in the vessel.
However, there are disadvantages associated with such conventional systems and methods for performing CVD. For example, using conventional CVD processes, the temperature and pressure gradients may vary at different locations within the process vessel, causing the rate and amount of deposition of the vapor material to vary from substrate to substrate, dependent upon the location of the substrate within the process vessel. In some conventional systems, vapor material release is poorly controlled and may not be uniformly applied to the substrate. For example, exit apertures may become clogged. Although in some instances, a clogged tube may be re-machined to unclog the holes, in many cases, replacement of the tube is necessary, limiting the useful life of the tube. Accordingly, there is a need for gas injection systems that provide better control and distribution of vapor material in CVD processes and for gas injection systems that may be reused more readily.